It was recently argued that the matrix can be both spatial or non-spatial. Accordingly, several proposals have been made in the literature, such as using the technological similarities or the transport costs instead of spatial metrics. One of the newest suggestions, however, is to analyze the effect of network-propagation, viewed both as an alternative and a complement to the spatial effect.
[1]} discuss the possibility of jointly modeling spatial and non-spatial dependence through a double autoregressive component that make use of two different weight matrix specifications [2]}.
In general, network theory and spatial econometrics are intimately connected. [3]} proposes using Spatial Autoregressive models employing an ad-hoc \(W\)  matrix based on network relations (in terms of social influences and communication); [4]} analyze the relationship between the topology property of networks and the properties of spatial models, performing several simulation tests.
[5]} gives a seminal contribution, as it lays the foundation for analyzing the exogenous, endogenous and correlated effects that researchers encounter both in network and econometric theory.
[6]}, following [5]}'s work, propose a specification for estimating network models in presence of exogenous, endogenous and correlated effects. Furthermore, the correct specification for the estimation of network models has become a popular object of study as of late [8]}, [9]}.
